Multiple Choice
You write MapReduce job to process 100 files in HDFS. Your MapReduce algorithm uses TextInputFormat: the mapper applies a regular expression over input values and emits key-values pairs with the key consisting of the matching text, and the value containing the filename and byte offset. Determine the difference between setting the number of reduces to one and settings the number of reducers to zero.
A) There is no difference in output between the two settings.
B) With zero reducers, no reducer runs and the job throws an exception. With one reducer, instances of matching patterns are stored in a single file on HDFS.
C) With zero reducers, all instances of matching patterns are gathered together in one file on HDFS. With one reducer, instances of matching patterns are stored in multiple files on HDFS.
D) With zero reducers, instances of matching patterns are stored in multiple files on HDFS. With one reducer, all instances of matching patterns are gathered together in one file on HDFS.
Correct Answer:
Verified
Correct Answer:
Verified
Q26: For each intermediate key, each reducer task
Q27: A combiner reduces:<br>A) The number of values
Q28: A client application creates an HDFS file
Q29: In a MapReduce job, you want each
Q30: MapReduce v2 (MRv2/YARN) splits which major functions
Q31: When can a reduce class also serve
Q32: In a MapReduce job, the reducer receives
Q34: All keys used for intermediate output from
Q35: You have user profile records in your
Q36: On a cluster running MapReduce v1 (MRv1),